The Cosmic Background Radiation

We review the current status of experimental data for spectral distortions and angular anisotropies of the cosmic microwave background, as well as discussing the relevant physical processes. This is one of a number of new articles in astrophysics and cosmology which will appear in the 1996 Review of Particle Properties (Phys. Rev. D. in press). Other relevant reviews include: "Big-Bang Cosmology" by K.A. Olive; "Big-Bang Nucleosynthesis" by K.A. Olive & D.N. Schramm; "The Hubble Constant" by C.J. Hogan; "Dark Matter" by M. Srednicki; "Cosmic Rays" by T.K. Gaisser & T. Stanev; "Solar Neutrinos" by K. Nakamura. Additional information is also available, such as astrophysical and cosmological constraints on particles such as axions and neutrinos, as well as tables of physical constants and astrophysical constants. These articles are part of a new initiative to widen the scope of the RPP by providing a regular review of some important topics and parameters in astrophysics.